1. Field of the Invention
The present invention relates to a light emitting device using a light emitting element which emits light when a current is supplied. In particular, the invention relates to a light emitting device which has a light emitting element having a layer containing an organic material and which realizes full color display by using a color conversion layer.
2. Description of the Related Art
Development has been made on a light emitting device which has a layer containing an organic material sandwiched between a pair of electrodes and has a light emitting element which emits light when a current is supplied between the electrodes. Such a light emitting device is advantageous in realizing thinness and lightweight as compared to other display devices which are called thin display devices. In addition, being self-luminous type, such a light emitting device has favorable visibility and fast response speed. Moreover, it is potentially possible to reduce power consumption considerably. Such a light emitting device is actively developed and put into practical use in some markets as a next-generation display.
There are some methods to realize such a light emitting device capable of performing full color display. One method is to deposit materials which exhibit light emission of each red, green, and blue separately by using a mask to manufacture a light emitting element which emits each color, another method is to use color filters of red, green, and blue for a light emitting element which exhibits white light emission to obtain light emission of three colors, and another method is convert mono-color light with a short wavelength into a required color through a color conversion layer. These methods are called a separate deposition method, a color filter (CF) method, and a color conversion method respectively for convenience.
Each of the three methods has advantages and disadvantages. It is a great advantage of the color conversion method to require no separate deposition of light emitting layers since light of only one color is emitted from a light emitting element. Moreover, the color conversion method is considered more efficient since desired light emission is obtained by using absorption of light, excitation, and light emission by a color conversion layer as compared to a CF method in which a part of a light emission spectrum is simply cut.
However, the efficiency of the color conversion method is still low as compared to the separate deposition method in which three colors are directly emitted from respective light emitting elements, and that the color conversion method is researched for further improvement in efficiency (for example, see Patent Documents 1 and 2).
[Patent Document 1]
Japanese Patent-Document Laid-open No. 2002-359076
[Patent Document 2]
Published Japanese Translation of PCT International Publication for Patent Application No. 2002-520801
According to the methods disclosed in these patent documents, a micro resonant structure formed of a dielectric mirror which is formed outside a light emitting element is used to improve the directivity of light and increase the amount of incident light to a color conversion layer (Patent Document 1), or a light emission peak is matched with an absorption peak of a color conversion layer (Patent Document 2) to improve the efficiency.
In the case of providing a micro resonant structure outside a light emitting element as disclosed in Patent Documents 1 and 2, light emitted from the light emitting element is required to pass through an electrode formed of a light-transmissive conductive film to reach the micro resonant structure. As a result, loss of the light decreases the efficiency.